1. Field of the Invention
The present invention relates to a surface acoustic wave resonator and a manufacturing method thereof, and more specifically, to a surface acoustic wave resonator and a manufacturing method thereof, which will be used for signal filtering or the like needed for signal processing of a wireless communication device.
2. Description of Related Art
As a device using surface acoustic waves, a surface acoustic wave (SAW) device, which has a comb-shaped electrode and a reflection electrode configured of an InterDigital Transducer (IDT) formed on the surface of a piezoelectric substrate and uses surface acoustic waves generated by applying power to the comb-shaped electrode, is well known to people. Since the SAW device is miniaturized and light-weighted and may obtain high attenuation, it is widely used in a Tx/Rx filter, an antenna duplexer or the like of a cellular phone terminal.
In the SAW device, a comb-shaped electrode and a reflection electrode made of, for example, aluminum are formed on a piezoelectric substrate made of Lithium Tantalate (LiTaO3), and a protection layer configured of a silicon oxide (SiO2) layer or the like is formed to cover the comb-shaped electrode and the reflection electrode. The silicon oxide (SiO2) protection layer is also a layer for temperature compensation.
If a SAW device is used, advantages described below can be obtained. A SAW resonator is advantageous in that its resonance frequency is ten times or more (direct oscillation of 100 MHz to 2 GHz is possible) higher than that of an existing bulk acoustic wave resonator although the quality factor Q is a little bit inferior. A frequency of a signal needs to be increased to process the information quantity of mobile communication steadily increasing in the present, and a further precise reference frequency is needed accordingly. Since the SAW resonator may obtain a reference frequency a few times higher, it is relatively advantageous in lowering power consumption and reducing the size.
In addition, since a resonance frequency of a SAW resonator is determined by a metal pattern of a crystal surface, it is advantageous in that elements of a uniform characteristic can be mass-produced using a thin-film process of the present IC process. The SAW resonator has an advantage of being integrated with a digital temperature compensation circuit for controlling the frequency on the background of compatibility with the IC process, and the possibility of reducing power consumption increases compared with an existing analog control method.
FIG. 1 is a view showing a temperature compensated SAW (TC-SAW) resonator of the prior art.
Referring to FIG. 1, a temperature compensated SAW (TC-SAW) resonator 10 includes a plurality of metal structures 12 on a piezoelectric substrate (LiNbO3) 11 and has a form of covering the piezoelectric substrate and the metal structures with a temperature compensation layer 13. At this point, the metal structure has a positive profile of 70 to 89 degrees.
However, it is required to develop a temperature compensated SAW resonator having a characteristic of a semi-resonance Q value (a Quality factor) higher than that of a conventional metal structure having such a profile and having a frequency characteristic insensitive to change of profile.